This invention relates generally to flexible tubes, and particularly to flexible tubes of the type having limited springback tendencies.
Flexible tubing made of rubber and cloth has been in existence for many years. Early attempts at improving their flexibility without an accompanying degradation in strength were directed at providing corrugations as exemplified by that disclosed in U.S. Pat. No. 314,440. Later, corrugations were formed in drinking tubes or straws to increase their flexibility as shown in U.S. Pat. No. 2,094,268.
Early tubular corrugations typically took a helical configuration. More recently, however, with the advent of thermoplastic materials, new configurations in corrugations have been made in an effort to simplify manufacture. For example, discontinuous grooves have been provided in flexible sections of thermoplastic drinking tubes as disclosed by U.S. Pat. No. 3,438,578. The material thickness in area of corrugations has also been varied to improve axial and radial flexibility as shown by U.S. Pat. No. 3,346,187.
Though the just described corrugated tubes have had good flexibility and strength, they have, by and large, been characterized by a high degree of resilience. Thus, once flexed or bent they have tended to reassume their originally constructed configuration unless held bent by ancillary holding means. In many situations, however, it is desirable to have the flexible tubing exhibit minimum springback tendencies once bent from its original configuration and thereby retain its bent configuration. Recently, new corrugations have been devised in efforts to overcome this problem of springback in drinking tubes as disclosed in U.S. Pat. Nos. 3,409,224, 3,445,552, and 3,908,704. The corrugations here are formed at skewed angles with the tube axes and with each corrugation defined by a groove having sides of unequal lengths. These unequal sides are joined together at the base of each groove at either a sharp angle therewith or with a close U-shape bend. The outside edges or ridges of corrugations have similar degrees of surface sharpness or roughness.
Though the just described flexible tubes have functioned relatively well, they have not been without disadvantages. For example, though a drinking tube or straw may incorporate only a relatively small flexible zone of the type described in an otherwise smooth tube, the ruffled outside edges of the corrugations have tended to impede their packaging into encapsulating paper covers. The straws are ordinarily sealed within paper jackets or covers by wrapping machines. The ruffled straw edges have caused excessively high rates of crinkling and jamming of the covers during machines wrapping operations to occur. In addition, to effect a bend of a given angle a predetermined number of grooves is required, which number has heretofore been rather large. The ruffled, peripheral surface of the flexible zone has also caused the drinking tubes or straws to become mutually interlocked rendering it difficult to process them during automatic packaging operations. Furthermore, when stored in hoppers these corrugations have also tended to reduce the degree of compactness with which large number of straws may be stored or processed.
Accordingly, it is a general object of the present invention to provide an improved flexible tube.
More specifically, it an object of the invention to provide an improved flexible tube of the type capable of retaining a bent configuration without appreciable springback tendency.
Another object of the invention is to provide a flexible tube of the type described having relatively smooth interior and exterior surfaces.
Another object of the invention is to provide a flexible tube of the type described requiring a relatively few number of circumferential grooves for effecting bends of selected angles.
Another object of the invention is to provide a flexible tube of the type described having minimal tendency to interlock with other tubes of the same configuration when stored in mutual abutment.
Yet another object of the invention is to provide a flexible tube of the type described capable of being stored in mass with an improved degree of compactness.